Ink jet printers are relatively inexpensive machines using non-impact methods to print. Print quality refers to characteristics, such as print sharpness, and is dependent, in part, on the mechanical design of ink jet printers and inks used during printing processes. The physical and chemical characteristics of inks, which affect print quality, may be altered by factors such as solvents, colorants and/or other ink additives. Colorants provide tints to inks and refer to dyes, dispersed dyes, or pigments. Dyes refer to colorants that are soluble during ink formation and printing. Pigments refer to colorants that are insoluble during ink formation and printing. Dispersed dyes refer to colorants that are insoluble during ink formation but become soluble some point during a printing process. Print quality is enhanced when colorants, such as pigments, are well dispersed in inks.
Dispersants attached to insoluble particles enhance the dispersion of insoluble particles in liquids and are sometimes characterized as one or more blocks of polymerized monomers. Hydrophobic blocks, which include polymerized monomers hydrophobic in nature, are involved in the binding of polymer dispersants to insoluble particles. Group transfer polymerization (GTP), can not be used to prepare block copolymers when monomers containing active hydrogens of the type present in primary amines are used as starting materials. Consequently, U.S. Pat. No. 5,272,201 (Ma et al.) discloses the use of a specific initiator for placing a monomer including an amine group at the beginning of a hydrophobic block and a method that forms a hydrophobic block with one or more tertiary amine groups placed within the ends of the hydrophobic block. Polymer dispersants disclosed in U.S. Pat. No. 5,272,201, have in addition to a hydrophobic block, a hydrophilic block that facilitates polymer dispersants' interactions with surrounding liquids. Consequently, a hydrophobic and a hydrophilic block each provide unique characteristics to a polymer dispersant. Modifications made to a hydrophobic block may affect the characteristics of a polymer dispersant differently than modifications made to a hydrophilic block, with each block playing a different role in the dispersion of insoluble particles (attachment versus liquid interaction).
Having a well dispersed ink prevents agglomeration, and settling to the bottom of a pigment, during the printing process. Other ink characteristics include the ability of an ink to bind to paper. Inks that bind well to paper are especially suited for specific applications such as use in high speed ink jet printers because they prevent smearing especially when the printed ink is touched by subsequent printed pages. The ability of an ink to bind to a substrate may be measured by a waterfastness test. An ink drop is applied to a substrate (such as paper) to form a spot. After a specific period of time, the substrate and ink are placed in contact with water. The substrate and ink are visually inspected to determine if the spot, formed by the drop of ink, smears in the presence of water. Another test for measuring the strength of ink binding to a substrate is called the mechanical smear test that requires rubbing the surface of a printed ink with a highlighter.